Inter-Band Handover of the Same Physical Frequency

ABSTRACT

A method of an access network node of a carrier aggregation enabled cellular wireless communication system, and a method of a wireless terminal device of a carrier aggregation enabled cellular wireless communication system are disclosed. The method for the network node comprises identifying a need for an inter-band handover where a same physical frequency on which the access network node interacts with a wireless terminal device has more than one logical reference, wherein the wireless terminal device currently operates using a first logical reference, assigning a target frequency for the inter-band handover as a second logical reference for the physical frequency, and performing handover signalling with the wireless terminal device including the assigned target frequency. The method of the wireless terminal device comprises performing operation where a need for an inter-band handover occurs where a same physical frequency on which the wireless terminal device interacts with an access network node of the cellular wireless communication system has more than one logical reference, wherein the wireless terminal device currently operates using a first logical reference, and performing handover signalling with the access network node including receiving an assigned target frequency which is a second logical reference for the physical frequency. A network node, a wireless terminal device and computer programs for these for implementing the methods are also disclosed.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 16/328,390, which was filed on Feb. 26, 2019, which is anational stage application of PCT/EP2016/070609, which was filed Sep. 1,2016, the disclosures of each of which are incorporated herein byreference in their entirety.

TECHNICAL FIELD

The present invention generally relates to a method of an access networknode of a carrier aggregation enabled cellular wireless communicationsystem, and a method of a wireless terminal device of a carrieraggregation enabled cellular wireless communication system, andcorresponding access network node, wireless terminal device and computerprograms for them. In particular, the method for the network nodecomprises identifying a need for an inter-band handover where a samephysical frequency on which the access network node interacts with awireless terminal device has more than one logical reference, whereinthe wireless terminal device currently operates using a first logicalreference, assigning a target frequency for the inter-band handover as asecond logical reference for the physical frequency, and performinghandover signalling with the wireless terminal device including theassigned target frequency. The method of the wireless terminal devicecomprises performing operation where a need for an inter-band handoveroccurs where a same physical frequency on which the wireless terminaldevice interacts with an access network node of the cellular wirelesscommunication system has more than one logical reference, wherein thewireless terminal device currently operates using a first logicalreference, and performing handover signalling with the access networknode including receiving an assigned target frequency which is a secondlogical reference for the physical frequency.

BACKGROUND

Carrier aggregation is one approach for enhancing capacity in a wirelesscommunication system. The aggregation of carriers provides increasedbandwidth to use for a connection. On the other hand, the possibility tocarrier aggregation also implies additional complexity in sense of setupand signalling.

EP 2343946 A2 discloses an approach where a set of logical channelpriorities are sent from an access network node to a wireless terminaldevice, wherein the wireless terminal device selects carriers based onthe logical channel priorities.

A problem that may arise is reliability in operation when setting up thecarrier aggregation communication. In particular, some actions forsetting up the carrier aggregation communication may increase the riskfor lost connection between access network node and wireless terminaldevice. It is therefore desired to provide a solution which decreasessuch risk.

SUMMARY

The invention is based on the inventors' realization that in somecommunication systems relations between logical references tofrequencies and the actual physical frequencies are not alwaysone-to-one. The inventors have further realized that not all logicalreferences are feasible for carrier aggregation operation. The inventorshave therefore suggested a solution utilizing regular handoveroperations in a special way for providing reliable transitions betweensingle carrier operation and carrier aggregation operation.

According to a first aspect, there is provided a method of an accessnetwork node of a carrier aggregation enabled cellular wirelesscommunication system. The method comprises identifying a need for aninter-band handover where a same physical frequency on which the accessnetwork node interacts with a wireless terminal device has more than onelogical reference, wherein the wireless terminal device currentlyoperates using a first logical reference. The method further comprisesassigning a target frequency for the inter-band handover as a secondlogical reference for the physical frequency, and performing handoversignalling with the wireless terminal device including the assignedtarget frequency.

The identifying may include identifying a carrier aggregation frequencyset including the second logical reference.

The logical references may be EUTRA Absolute Radio-Frequency ChannelNumber, EARFCN.

The performing of the handover signalling may comprise sending ameasurement configuration to the wireless terminal device including thesecond logical reference.

The method may comprise performing the handover such that the wirelessterminal device operates on the physical frequency using the secondlogical reference after the handover.

According to a second aspect, there is provided a network node of anaccess network of a carrier aggregation enabled cellular wirelesscommunication system, wherein the network node is arranged to identify aneed for an inter-band handover where a same physical frequency on whichthe network node interacts with a wireless terminal device has more thanone logical reference, wherein the wireless terminal device currentlyoperates using a first logical reference. The network node is furtherarranged to assign the target frequency for the inter-band handover as asecond logical reference for the physical frequency, and to performhandover signalling with the wireless terminal device including theassigned target frequency.

The network node may be arranged to identify a carrier aggregationfrequency set including the second logical reference.

The logical references may be EUTRA Absolute Radio-Frequency ChannelNumber, EARFCN.

The handover signalling may comprise a measurement configurationtransmission to the wireless terminal device including the secondlogical reference.

The network node may be arranged to perform the handover such that thewireless terminal device operates on the physical frequency using thesecond logical reference after the handover.

According to a third aspect, there is provided a computer programcomprising instructions which, when executed on a processor of a networknode of an access network of a carrier aggregation enabled cellularwireless communication system, causes the network node to perform themethod according to the first aspect.

According to a fourth aspect, there is provided a method of a wirelessterminal device of a carrier aggregation enabled cellular wirelesscommunication system. The method comprises performing operation where aneed for an inter-band handover occurs where a same physical frequencyon which the wireless terminal device interacts with an access networknode of the cellular wireless communication system has more than onelogical reference, wherein the wireless terminal device currentlyoperates using a first logical reference, and performing handoversignalling with the access network node including receiving an assignedtarget frequency which is a second logical reference for the physicalfrequency.

The method may further comprise analysing mapping of the first andsecond logical references to observe that they relate to the samephysical frequency, and, when observed that they relate to the samephysical frequency, recovering measurement values made for the firstlogical reference and assigning the measurement values for the secondlogical reference.

The logical references may be EUTRA Absolute Radio-Frequency ChannelNumber, EARFCN.

The performing of the handover signalling may comprise receiving ameasurement configuration including the second logical reference.

The method may comprise performing the handover such that the wirelessterminal device operates on the physical frequency using the secondlogical reference after the handover.

According to a fifth aspect, there is provided a wireless terminaldevice of a carrier aggregation enabled cellular wireless communicationsystem. The wireless terminal device is arranged to perform operationwhere a need for an inter-band handover occurs where a same physicalfrequency on which the wireless terminal device interacts with an accessnetwork node of the cellular wireless communication system has more thanone logical reference, wherein the wireless terminal device currentlyoperates using a first logical reference, and perform handoversignalling with the access network node including receiving an assignedtarget frequency which is a second logical reference for the physicalfrequency.

The wireless terminal device may be arranged to analyse mapping of thefirst and second logical references to observe that they relate to thesame physical frequency, and, when observed that they relate to the samephysical frequency, recover measurement values made for the firstlogical reference and assign the measurement values for the secondlogical reference.

The logical references may be EUTRA Absolute Radio-Frequency ChannelNumber, EARFCN.

The handover signalling may include to receive a measurementconfiguration including the second logical reference.

The wireless terminal device may be arranged such performing of thehandover is such that the wireless terminal operates on the physicalfrequency using the second logical reference after the handover.

According to a sixth aspect, there is provided a computer programcomprising instructions which, when executed on a processor of awireless terminal device of a carrier aggregation enabled cellularwireless communication system, causes the wireless terminal device toperform the method according to the fourth aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as additional objects, features and advantages of thepresent invention, will be better understood through the followingillustrative and non-limiting detailed description of preferredembodiments of the present invention, with reference to the appendeddrawings.

FIG. 1 schematically illustrates principles of carrier aggregation.

FIG. 2 is a flow chart schematically illustrating a method of an accessnetwork node according to embodiments.

FIG. 3 is a flow chart schematically illustrating a method of an accessnetwork node according to embodiments.

FIG. 4 is a block diagram schematically illustrating an access networknode according to an embodiment.

FIG. 5 is a flow chart schematically illustrating a method of a wirelessterminal device according to embodiments.

FIG. 6 is a block diagram schematically illustrating a wireless terminaldevice according to an embodiment.

FIG. 7 schematically illustrates a computer-readable medium and aprocessing device.

FIG. 8 schematically illustrates a cellular wireless network.

DETAILED DESCRIPTION

Carrier aggregation is used for providing increased bandwidth comparedwith single carriers provided by a communication system, e.g. theevolved UMTS (Universal Mobile Telecommunications System) TerrestrialRadio Access (EUTRA). For example, the LTE Rel-10 standard can therebysupport bandwidths larger than 20 MHz. One important requirement on LTERel-10 is to assure backward compatibility with LTE Rel-8, which onlysupports single carrier operation. This should also include spectrumcompatibility. That would imply that an LTE Rel-10 carrier, wider than20 MHz, should appear as a number of LTE carriers to an LTE Rel-8terminal. Each such carrier can be referred to as a Component Carrier(CC). In particular for early LTE Rel-10 deployments it can be expectedthat there will be a smaller number of LTE Rel-10-capable terminalscompared to many LTE legacy terminals. Therefore, it is necessary toassure an efficient use of a wide carrier also for legacy terminals,i.e. that it is possible to implement carriers where legacy terminalscan be scheduled in all parts of the wideband LTE Rel-10 carrier. Thestraightforward way to obtain this would be by means of CarrierAggregation (CA). CA implies that an LTE Rel-10 terminal can receivemultiple CC, where the CC have, or at least the possibility to have, thesame structure as a Rel-8 carrier. CA is illustrated in Fig. XX. ACA-capable UE is assigned a primary cell (PCell) which is alwaysactivated, and one or more secondary cells (SCells) which may beactivated or deactivated dynamically.

It is to be noted that the terms “UE”, “terminal”, “mobile device”, etc.are in colloquial language meaning the same item, i.e. a wirelessterminal device, and are interchangeably used in this disclosure.

The number of aggregated CC as well as the bandwidth of the individualCC may be different for uplink and downlink. A symmetric configurationrefers to the case where the number of CCs in downlink and uplink is thesame whereas an asymmetric configuration refers to the case that thenumber of CCs is different. It is important to note that the number ofCCs configured in a cell may be different from the number of CCs seen bya terminal: A terminal may for example support more downlink CCs thanuplink CCs, even though the cell is configured with the same number ofuplink and downlink CCs.

Downlink transmissions are dynamically scheduled, i.e., in each subframethe base station transmits control information about which terminalsdata is transmitted to and upon which resource blocks the data istransmitted, in the current downlink subframe. This control signallingis typically transmitted in the first 1, 2, 3 or 4 OFDM symbols in eachsubframe and the number n=1, 2, 3 or 4 is known as the Control FormatIndicator (CFI). The downlink subframe also contains common referencesymbols, which are known to the receiver and used for coherentdemodulation of e.g. the control information.

A Physical Downlink Control CHannel (PDCCH) is used to carry downlinkcontrol information (DCI) such as scheduling decisions and power-controlcommands. More specifically, the DCI includes:

-   -   Downlink scheduling assignments, including Physical Downlink        Shared Channel (PDSCH) resource indication, transport format,        hybrid-ARQ (Automatic Repeat reQuest) information, and control        information related to spatial multiplexing (if applicable). A        downlink scheduling assignment also includes a command for power        control of the PUCCH used for transmission of hybrid-ARQ        acknowledgements in response to downlink scheduling assignments.    -   Uplink scheduling grants, including Physical Uplink Shared        Channel (PUSCH) resource indication, transport format, and        hybrid-ARQ-related information. An uplink scheduling grant also        includes a command for power control of the PUSCH.    -   Power-control commands for a set of terminals as a complement to        the commands included in the scheduling assignments/grants.

One PDCCH carries one DCI message containing one of the groups ofinformation listed above. As multiple terminals can be scheduledsimultaneously, and each terminal can be scheduled on both downlink anduplink simultaneously, there must be a possibility to transmit multiplescheduling messages within each subframe. Each scheduling message istransmitted on separate PDCCH resources, and consequently there aretypically multiple simultaneous PDCCH transmissions within each subframein each cell. Furthermore, to support different radio-channelconditions, link adaptation can be used, where the code rate of thePDCCH is selected by adapting the resource usage for the PDCCH, to matchthe radio-channel conditions.

In addition, a feature of carrier aggregation is the ability to performcross-carrier scheduling. This mechanism allows a (e)PDCCH on one CC toschedule data transmissions on another CC by means of a 3-bit CarrierIndicator Field (CIF) inserted at the beginning of the (e)PDCCHmessages. For data transmissions on a given CC, a UE expects to receivescheduling messages on the (e)PDCCH on just one CC—either the same CC,or a different CC via cross-carrier scheduling; this mapping from(e)PDCCH to PDSCH is also configured semi-statically. Herein, “e” and“(e)” is used for indicating particular and possible particular featuresfor “evolved” or “enhanced” formats, i.e. particularly adapted for theLTE.

3GPP TS 36.101, V13.2.1, specifies UE requirements for certain bandcombinations. A UE sends its capabilities including some of these bandcombinations to eNB, which is then restricted to use those. The mappingbetween bands and physical frequencies as specified in TS 36.101,V13.2.1, is not unique. That is, more than one band can map to the sameor a subset of physical frequencies, for example as the case of Band 1and Band 4.

Due to this unambiguity, the eNB is sometimes forced to logically move aUE from one band to another to allow carrier aggregation. One way to dothis while still keeping the connection to the UE is to instruct the UEto perform a handover to the same cell but on a different logical band.Note that a Rel-11 UE is required to attach to a cell on the first bandit supports, and thus the only way for such a UE to have a PCell on asecondary band is through RRC signalling (handover).

For example for cells on band 38 (which has additional band 41) and band39, inter band carrier aggregation is not possible as there is nocarrier aggregation combination for band 38+39 defined in TS 36.101. AUE has to attach to primary band of a cell (if UE supports it). So if UEsupports both band 38 and band 41, no carrier aggregation is possibleunless eNB orders an intra-cell handover to additional band 41, whichhas a valid band combination with band 39.

Another limitation can be total bandwidth. The combination band 17+band2 has a total max bandwidth of 20 MHz. So to enable carrier aggregationfor two cells with e.g. bandwidth 10+15 MHz it is possible to use band12 (additional to band 17) and band 2, which has higher possible maxbandwidth.

When the UE performs a handover to a different logical frequency, e.g. anotation such as EUTRA Absolute Radio-Frequency Channel Number (EARFCN),it will typically not keep cell measurements (timing, frequencycorrections, RSRP, RSRQ etc.) from the source EARFCN even if they arethe same physical frequency and thus have the same cells present. Thiswill result in a blind handover were the UE first has to establish timeand frequency synch to the target cell (which in this case is the sameas the source cell). During this procedure there is a risk of failingthe RACH procedure and end up in a re-establishment or droppedconnection. By configuring the UE to measure the target logicalreference, e.g. EARFCN (which physically maps to the same physicalfrequency as the source EARFCN), as an inter-frequency carrier, the UEcan establish time and frequency synchronization to the target cellbefore performing the handover. According to one embodiment, the UEanalyses the mapping between the logical frequency and the physicalfrequency and when discovered that the physical frequency is the samefor two logical frequencies, i.e. the logical frequency before handoverand the target logical frequency, the UE keeps any measurement valuesand assigns them to the target logical frequency.

Even if the UE does not have the capability demonstrated for theembodiment above, the eNB may know that results of measurements ontarget logical frequency will, is fairly static environment, be the sameas for the logical frequency before handover, and a stable andpredictable behaviour of the inter band handover is beforehand known.

Thus, the present disclosure will be applicable for cases where both theeNB and UEs are capable of the here suggested solutions, but will alsobe applicable where only the eNB is capable of the here suggestedsolutions, i.e. legacy UEs will still benefit from the solution,although UEs capable of some of the here suggested solutions benefitfrom e.g. reduced energy consumption, faster processing, etc. at theinter band handover.

FIG. 2 is a flow chart illustrating methods of an access network node ofa carrier aggregation enabled cellular wireless communication system.The access network node identifies 200 a need for an inter-bandhandover. This is where a same physical frequency on which the accessnetwork node interacts with a wireless terminal device has more than onelogical reference, and the wireless terminal device is currentlyoperating using a first logical reference. The access network nodeassigns 202 a target frequency for the inter-band handover as a secondlogical reference for the same physical frequency, and performs 204handover signalling with the wireless terminal device including theassigned target frequency. Thus, the access network node will providefor enabling carrier aggregation operation where the first logicalreference is not available for carrier aggregation, but by an inter-bandhandover to the same physical frequency, the physical frequency can beincluded in the carrier aggregation operation. That is, the performing204 of the handover is made such that the wireless terminal deviceoperates on the same physical frequency but using the second logicalreference after the handover.

The identifying 200 may include identifying a carrier aggregationfrequency set including the second logical reference. This is forexample made from a look-up table. The logical references may be EARFCN.

The performing 204 of the handover signalling may for example includesending a measurement configuration to the wireless terminal deviceincluding the second logical reference. That is, established handovermechanisms, e.g. the measurement configuration mentioned here, may beused for the inter-band handover ending with carrier aggregation at thesame physical frequency.

Here, it may be noted that steps 200 and 202 are preferably performedjointly, from a timing point of view, since the interaction betweenassigning 202 the logical reference and identifying 200 the need forinter-band handover depends on each other in sense of the feasiblelogical frequency references for carrier aggregation.

FIG. 3 is a flow chart illustrating a method of an access network nodeaccording to an embodiment. While the operations demonstrated withreference to FIG. 2 on a general level, the operations demonstrated withreference to FIG. 3 are to be considered one more detailed embodimentthereof.

The access network node determines 300 frequencies to use in carrieraggregation operation. This includes determining the logical referencesfor the frequencies, i.e. what logical references are feasible forcarrier aggregation from a scheme defined for the communication network.Here, the access network node selects one of the logical references suchthat the physical frequency to which it refers is the same as thephysical frequency currently used, if possible, which physical frequencymay have another logical reference when operating in single carriermode. The access network node then determines 302 whether there is aneed for inter-band handover, i.e. if the logical reference of thecurrently used frequency is not feasible for the carrier aggregation. Ifthe logical reference of the currently used frequency is feasible forthe carrier aggregation, i.e. there is no need for inter-band handover,the procedure simply continues with carrier aggregation operation 316.That is, the logical reference in single carrier mode is also applicablein carrier aggregation mode, wherein the carrier aggregation operation316 may commence using the same logical reference. Otherwise, aninter-band handover procedure 304-314 is performed, where the physicalfrequency is maintained, but with another logical reference. The logicalreferences may for example be EARFCN.

Optionally, it is checked 304 whether the UE requires measurement gaps,and if so, measurement gaps are configured 306. For example, the UE hassignalled a capability indicating the requirement of gaps for it to beable to perform Radio Resource Management (RRM) measurements, whereinthe access network node makes a measurement gap configuration andsignals to the UE, e.g. by MeasGapConfig message.

The access network node configures 308 a target logical reference onwhich measurements are to be made, e.g. by MeasObjectEUTRA, and signalsit to the UE. The signalling may comprise the target EARFCN and thesource EARFCN, which both refer to a same physical frequency althoughlogically being considered as different frequencies. To avoid reports ofother cells on this frequency, which is not the intention of theoperation, the access network node may for example configure anindicator (PCI) of the Primary Cell (PCell) in a white-list, whichindicates preferred cell on which measurements should be made, orconfigure other known neighbour cells in a black-list, which indicatescells to be omitted from measurements.

Optionally, the access network node configures 310 measurement eventsfor the UE, e.g. A3 and/or A4. A3 is an event for triggering that aneighbour cell is a certain dB stronger than the PCell. Here, since theneighbour cell and the PCell are the same, but with different logicalreferences, a reported Reference Signal Received Power (RSRP) shouldreasonably be about the same and a fairly small offset may be used. Itis further to be noted that if the UE measures the cell, the reportedvalue may differ slightly if the receiver happens to be configureddifferently compared with when the measurement of the source cell wasmade. If the UE keep previously measured values, as demonstrated belowfor one embodiment of the UE, there should be no difference. A4 is anevent with an absolute criterion. A further alternative is that theconfiguration is made for periodic reporting. The configuration may besignalled as ReportConfigEUTRA to the UE. The access network node maythen wait for a measurement report from the UE and then proceeds.Alternatively, the access network node is configured only to wait apredetermined time before proceeding. The proceeding includes to perform314 the handover.

The procedure referred to as 304-310 above may be performed using a sameRRCConnectionReconfiguration message.

The access network node performs 314 the handover, wherein operation 316with carrier aggregation can commence.

FIG. 4 is a block diagram schematically illustrating an access networknode 400 according to an embodiment. The access network node 400comprises an antenna arrangement 402, a transceiver 404 connected to theantenna arrangement 402, and a processing element 406 which may compriseone or more circuits and is arranged to operate as a controller of theaccess network node 400. The access network node 400 may comprise one ormore input interfaces and/or one or more output interfaces arranged forenabling the access network node 400 to complete for example providingbackhaul towards one or more communication networks, e.g. by signalinterfaces, e.g. wireless, electrical or optical. The interfaces canalso include user interfaces for enabling user interaction, for examplefor maintenance or configuration. The access network node 400 isarranged to operate in a wireless communication network for enablingcommunication with one or more terminals, as illustrated in FIG. 8. Inparticular, by the processing element 406 being arranged to perform anyof the embodiments demonstrated with reference to FIG. 2 or 3, theaccess network node 400 is capable of enabling at least some of theinteracting terminals to operate more reliably and predictable wheninter-band handover is to be performed as demonstrated above, andpossibly also with limited energy consumption since some measurementprocedures may be omitted in some embodiments. The processing element406 can also fulfill a multitude of tasks, ranging from signalprocessing to enable reception and transmission since it is connected tothe transceiver 404, executing applications, controlling the interfaces,etc. In particular, the access network node 400 is enabled to operatewith terminals capable of carrier aggregation.

As will be demonstrated below, the UE may take certain actions forfacilitating the procedure at the UE end. However, the approach at theaccess network node is not depending on such actions. Interaction with alegacy UE will still provide advantages. Since it is well predictablethat the physical frequency is well working for connection between theaccess network node and the UE, there is provided a reliable transitionfrom single carrier operation to carrier aggregation operation. Ahandover operation to completely new physical frequency will not providethat predictability, and is thus not providing such reliability, withrisk of lost connection at stake.

It should be noted that the handover as demonstrated herein may bedeliberately omitted when low signal power and/or high interference isreported by the UE. In such cases, the established connection may not beput at stake for the additional bandwidth which may be gained from thecarrier aggregation operation. Reporting of signal power andinterference levels by the UE are preferably performed as commonlyperformed by legacy UEs. For example, the selection whether to omit theinter-band handover may be implemented by the reported signal powerand/or interference level being compared with respective thresholds fordetermining whether to enable the inter-band handover as demonstratedherein. The thresholds may be selected based on experience fromoperation, and the thresholds may be updated continuously orperiodically based on successful and unsuccessful inter-band handovers.The thresholds may also be fixed and set by a provider or an operator ofthe network.

FIG. 5 is a flow chart illustrating methods of a wireless terminaldevice of a carrier aggregation enabled cellular wireless communicationsystem. The wireless terminal device performs 500 operation where a needfor an inter-band handover occurs, as demonstrated above, where a samephysical frequency on which the wireless terminal device interacts withan access network node of the cellular wireless communication system hasmore than one logical reference. Thus, the wireless terminal devicecurrently operates 500 using a first logical reference. The wirelessterminal device performs 502 handover signalling with the access networknode including receiving an assigned target frequency which is a secondlogical reference for the physical frequency. Thus, the wirelessterminal device, in accordance with the signalling, performs handoveroperations to operate on the same physical frequency but with anotherlogical reference. This enables, where the first logical reference isnot feasible for carrier aggregation operation, that carrier aggregationoperation be performed, where the second logical reference is feasiblefor carrier aggregation, although the physical frequency is the same forboth the first and the second logical references. The performing 502 ofthe handover signalling may include receiving a measurementconfiguration including the second logical reference. That is,established handover mechanisms, e.g. the measurement configurationmentioned here, may be used for the inter-band handover ending withcarrier aggregation at the same physical frequency, i.e. performing thehandover 506 such that the wireless terminal device operates on the samephysical frequency using the second logical reference after thehandover.

The wireless terminal device may make measurements etc. according to thehandover signalling. However, according to some embodiments, thewireless terminal device may identify the situation and make someactions for limiting its efforts. The wireless terminal device may insuch cases analyse 503 mapping of the first and second logicalreferences to observe that they relate to the same physical frequency,and when observed that they relate to the same physical frequency,recover 505 measurement values made for the first logical reference andassigning the measurement values for the second logical reference. Here,it may be noted that the actions 503 and 505 are preferably performed inparallel with the handover operations 502 since the mutual informationexchange (logical reference to frequency, measurements) depends on eachother. By the recovering 505 of measurement values, the UE may save theenergy consumption for making the measurements. The analysis 503 may forexample be made by a table look-up, where the physical frequency of thefirst logical reference, as known from the operation 500, is comparedwith the physical frequency of the second logical reference, which isgiven from the handover signalling 502 and indicated by upper curvedarrow. When the physical frequency is the same, the recovering 505 isperformed and the recovered measurement values are provided to thehandover signalling 502, as indicated by lower curved arrow.

It should be noted that the approach for the wireless terminal devicedemonstrated above is particularly suitable for operating together withan access network node as demonstrated with reference to FIGS. 2 to 4.However, the approach including the optional steps 503 and 505 mayprovide benefits also when operating with legacy access network nodes,i.e. the recovering 505 of measurement values may save efforts also insituations occurring, and being identified by the analysis 503, whenoperating with the legacy access network node.

FIG. 6 is a block diagram schematically illustrating a wireless terminaldevice 600 according to an embodiment. The wireless terminal device orUE 600 comprises an antenna arrangement 602, a receiver 604 connected tothe antenna arrangement 602, a transmitter 606 connected to the antennaarrangement 602, a processing element 608 which may comprise one or morecircuits, one or more input interfaces 610 and one or more outputinterfaces 612. The interfaces 610, 612 can be user interfaces and/orsignal interfaces, e.g. electrical or optical. The UE 600 is arranged tooperate in a cellular communication network. In particular, by theprocessing element 608 being arranged to perform the embodimentsdemonstrated with reference to FIG. 5, the UE 600 is capable of reliablytransition from single carrier operation to carrier aggregationoperation also when the first logical reference is not feasible forcarrier aggregation operation. The processing element 608 can alsofulfil a multitude of tasks, ranging from signal processing to enablereception and transmission since it is connected to the receiver 604 andtransmitter 606, executing applications, controlling the interfaces 610,612, etc. Thus, the solid lines to/from the processor 608 indicateprovision of data, while the dotted line arrows indicate controlprovided by the processor 608.

The methods according to the present invention is suitable forimplementation with aid of processing means, such as computers and/orprocessors, especially for the case where the controller 406 orprocessing element 608 demonstrated above comprises a processor handlingthe approaches demonstrated with reference to FIGS. 2, 3 and 5,respectively. Therefore, there is provided computer programs, comprisinginstructions arranged to cause the processing means, processor, orcomputer to perform the steps of any of the methods according to any ofthe embodiments described with reference to FIGS. 2, 3 and 5. Thecomputer program preferably comprises program code which is stored on acomputer readable medium 700, as illustrated in FIG. 7, which can beloaded and executed by a processing means, processor, or computer 702 tocause it to perform the methods, respectively, according to embodimentsof the present invention, preferably as any of the embodiments describedwith reference to FIGS. 2, 3 and 5. The computer 702 and computerprogram product 700 can be arranged to execute the program codesequentially where actions of the any of the methods are performedstepwise, but may as well execute the actions on a real-time basis. Theprocessing means, processor, or computer 702 is preferably what normallyis referred to as an embedded system. Thus, the depicted computerreadable medium 700 and computer 702 in FIG. 7 should be construed to befor illustrative purposes only to provide understanding of theprinciple, and not to be construed as any direct illustration of theelements.

FIG. 8 illustrates a cellular wireless network comprising a moredetailed view of an access network node 800 and a communicationtransceiver 810, in accordance with a particular embodiment. Forsimplicity, FIG. 8 only depicts network 820, access network nodes 800and 800 a, and communication transceiver 810. Access network node 800comprises processor 802, storage 803, interface 801, and antenna set 801a. Similarly, the communication transceiver 810 comprises processor 812,storage 813, interface 811 and antenna set 811 a. These components maywork together in order to provide access network node and/or wirelessdevice functionality. In different embodiments, the wireless network maycomprise any number of wired or wireless networks, access network nodes,base stations, controllers, wireless devices, relay stations, and/or anyother components that may facilitate or participate in the communicationof data and/or signals whether via wired or wireless connections.

Network 820 may comprise one or more IP networks, public switchedtelephone networks (PSTNs), packet data networks, optical networks, widearea networks (WANs), local area networks (LANs), wireless local areanetworks (WLANs), wired networks, wireless networks, metropolitan areanetworks, and other networks to enable communication between devices.

Access network node 800 comprises processor 802, storage 803, interface801, and antenna set 801 a. These components are depicted as singleboxes located within a single larger box. In practice however, an accessnetwork node may comprise multiple different physical components thatmake up a single illustrated component (e.g., interface 801 may compriseterminals for coupling wires for a wired connection and a radiotransceiver for a wireless connection). Similarly, access network node800 may be composed of multiple physically separate components (e.g., aNodeB component and a Radio Network Controller (RNC) component, a BaseTransceiver Station (BTS) component and a Base Station Controller (BSC)component, etc.), which may each have their own respective processor,storage, and interface components. In certain scenarios in which accessnetwork node 800 comprises multiple separate components (e.g., BTS andBSC components), one or more of the separate components may be sharedamong several access network nodes. For example, a single RNC maycontrol multiple NodeB's. In such a scenario, each unique NodeB and BSCpair, may be a separate access network node. In some embodiments, accessnetwork node 800 may be configured to support multiple radio accesstechnologies (RATs). In such embodiments, some components may beduplicated (e.g., separate storage 803 for the different RATs) and somecomponents may be reused (e.g., the same antenna set 801 a may be sharedby the RATs).

Processor 802 may be a combination of one or more of a microprocessor,controller, microcontroller, central processing unit, digital signalprocessor, application specific integrated circuit, field programmablegate array, or any other suitable computing device, resource, orcombination of hardware, software and/or encoded logic operable toprovide, either alone or in conjunction with other access network node800 components, such as storage 803, access network node 800functionality. For example, processor 802 may execute instructionsstored in storage 803. Such functionality may include providing variouswireless features discussed herein to a wireless terminal device, suchas communication transceiver 810, including any of the features orbenefits disclosed herein.

Storage 803 may comprise any form of volatile or non-volatile computerreadable memory including, without limitation, persistent storage, solidstate memory, remotely mounted memory, magnetic media, optical media,random access memory (RAM), read-only memory (ROM), removable media, orany other suitable local or remote memory component. Storage 803 maystore any suitable instructions, data or information, including softwareand encoded logic, utilized by access network node 800. Storage 803 maybe used to store any calculations made by processor 802 and/or any datareceived via interface 801.

Access network node 800 also comprises interface 801 which may be usedin the wired or wireless communication of signalling and/or data betweenaccess network node 800, network 820, and/or communication transceiver810. For example, interface 801 may perform any formatting, coding, ortranslating that may be needed to allow access network node 800 to sendand receive data from network 820 over a wired connection. Interface 801may also include a radio transmitter and/or receiver that may be coupledto or a part of antenna set 801 a. The radio may receive digital datathat is to be sent out to other access network nodes or communicationtransceivers via a wireless connection. The radio may convert thedigital data into a radio signal having the appropriate channel andbandwidth parameters. The radio signal may then be transmitted viaantenna set 801 a to the appropriate recipient (e.g., communicationtransceiver 810).

Antenna set 801 a may be any type of antenna capable of transmitting andreceiving data and/or signals wirelessly. Here, the antenna set 801 a isto be considered as a plurality of antennas such that multi-ranktransmissions are enabled. In some embodiments, antenna set 801 a maycomprise two or more omnidirectional, sector or panel antennas operableto transmit/receive radio signals between, for example, 700 MHz and 66GHz. An omnidirectional antenna may be used to transmit/receive radiosignals in any direction, a sector antenna may be used totransmit/receive radio signals from devices within a particular area,and a panel antenna may be a line of sight antenna used totransmit/receive radio signals in a relatively straight line.

The communication transceiver 810 may be any type of communicationdevice, wireless device, UE, D2D device or ProSe (Proximity Service) UE,but may in general be any device, sensor, actuator, smart phone, modem,laptop, Personal Digital Assistant (PDA), tablet, mobile terminal, smartphone, laptop embedded equipped (LEE), laptop mounted equipment (LME),Universal Serial Bus (USB) dongles, machine type UE, UE capable ofmachine-to-machine (M2M) communication, etc., which is able towirelessly send and receive data and/or signals to and from a accessnetwork node, such as access network node 800 and/or other communicationtransceivers. The communication transceiver 810 comprises processor 812,storage 813, interface 811, and antenna 811 a. Like access network node800, the components of communication transceiver 810 are depicted assingle boxes located within a single larger box, however in practice awireless device may comprise multiple different physical components thatmake up a single illustrated component (e.g., storage 813 may comprisemultiple discrete microchips, each microchip representing a portion ofthe total storage capacity).

Processor 812 may be a combination of one or more of a microprocessor,controller, microcontroller, central processing unit, digital signalprocessor, application specific integrated circuit, field programmablegate array, or any other suitable computing device, resource, orcombination of hardware, software and/or encoded logic operable toprovide, either alone or in combination with other communicationtransceiver 810 components, such as storage 813, communicationtransceiver 810 functionality. Such functionality may include providingvarious wireless features discussed herein, including any of thefeatures or benefits disclosed herein.

Storage 813 may be any form of volatile or non-volatile memoryincluding, without limitation, persistent storage, solid state memory,remotely mounted memory, magnetic media, optical media, RAM, ROM,removable media, or any other suitable local or remote memory component.Storage 813 may store any suitable data, instructions, or information,including software and encoded logic, utilized by communicationtransceiver 810. Storage 813 may be used to store any calculations madeby processor 812 and/or any data received via interface 811.

Interface 811 may be used in the wireless communication of signallingand/or data between communication transceiver 810 and access networknode 800. For example, interface 811 may perform any formatting, coding,or translating that may be needed to allow communication transceiver 810to send and receive data from access network node 800 over a wirelessconnection. Interface 811 may also include a radio transmitter and/orreceiver that may be coupled to or a part of antenna 811 a. The radiomay receive digital data that is to be sent out to access network node801 via a wireless connection. The radio may convert the digital datainto a radio signal having the appropriate channel and bandwidthparameters. The radio signal may then be transmitted via antenna 811 ato access network node 800.

Antenna 811 a may be any type of antenna capable of transmitting andreceiving data and/or signals wirelessly. In some embodiments, antenna811 a may comprise one or more omnidirectional, sector or panel antennasoperable to transmit/receive radio signals between 2 GHz and 66 GHz. Forsimplicity, antenna 811 a may be considered a part of interface 811 tothe extent that a wireless signal is being used.

In some embodiments, the components described above may be used toimplement one or more functional modules used in D2D communication. Thefunctional modules may comprise software, computer programs,sub-routines, libraries, source code, or any other form of executableinstructions that are run by, for example, a processor. In generalterms, each functional module may be implemented in hardware and/or insoftware. Preferably, one or more or all functional modules may beimplemented by processors 812 and/or 802, possibly in cooperation withstorage 813 and/or 803. Processors 812 and/or 802 and storage 813 and/or803 may thus be arranged to allow processors 812 and/or 802 to fetchinstructions from storage 813 and/or 803 and execute the fetchedinstructions to allow the respective functional module to perform anyfeatures or functions disclosed herein. The modules may further beconfigured to perform other functions or steps not explicitly describedherein but which would be within the knowledge of a person skilled inthe art.

Certain aspects of the inventive concept have mainly been describedabove with reference to a few embodiments. However, as is readilyappreciated by a person skilled in the art, embodiments other than theones disclosed above are equally possible and within the scope of theinventive concept. Similarly, while a number of different combinationshave been discussed, all possible combinations have not been disclosed.One skilled in the art would appreciate that other combinations existand are within the scope of the inventive concept. Moreover, as isunderstood by the skilled person, the herein disclosed embodiments areas such applicable also to other standards and communication systems andany feature from a particular figure disclosed in connection with otherfeatures may be applicable to any other figure and or combined withdifferent features.

1. A method of operating an access network node of a carrier aggregationenabled cellular wireless communication system, wherein the network nodeinteracts with a wireless terminal device having more than one logicalreference on a same physical frequency, wherein the wireless terminaldevice currently operates using a first logical reference, the methodcomprising the network node: assigning a target frequency for theinter-band handover as a second logical reference for the physicalfrequency; and performing handover signaling with the wireless terminaldevice including the assigned target frequency.
 2. The method of claim1, wherein the logical references are evolved UMTS (Universal MobileTelecommunications System) Terrestrial Radio Access (EUTRA) AbsoluteRadio-Frequency Channel Number (EARFCN).
 3. The method of claim 1,wherein the performing the handover signaling comprises sending ameasurement configuration to the wireless terminal device including thesecond logical reference.
 4. The method of claim 1, further comprisingperforming the handover such that the wireless terminal device operateson the physical frequency using the second logical reference after thehandover.
 5. A network node of an access network of a carrieraggregation enabled cellular wireless communication system, wherein thenetwork node interacts with a wireless terminal device having more thanone logical reference on a same physical frequency, wherein the wirelessterminal device currently operates using a first logical reference, thenetwork node comprising: processing circuitry; memory containinginstructions executable by the processing circuitry whereby the networknode is operative to: assign the target frequency for the inter-bandhandover as a second logical reference for the physical frequency; andperform handover signaling with the wireless terminal device includingthe assigned target frequency.
 6. The network node of claim 5, whereinthe logical references are evolved UMTS (Universal MobileTelecommunications System) Terrestrial Radio Access (EUTRA) AbsoluteRadio-Frequency Channel Number (EARFCN).
 7. The network node of claim 5,wherein the handover signaling comprises a measurement configurationtransmission to the wireless terminal device including the secondlogical reference.
 8. The network node of claim 5, wherein theinstructions are such that the network node is operative to perform thehandover such that the wireless terminal device operates on the physicalfrequency using the second logical reference after the handover.
 9. Amethod of operating a wireless terminal device of a carrier aggregationenabled cellular wireless communication system, where a same physicalfrequency on which the wireless terminal device interacts with an accessnetwork node of the cellular wireless communication system has more thanone logical reference, the method comprising the wireless terminaldevice: performing an operation where a need for an inter-band handoveroccurs, wherein the wireless terminal device currently operates using afirst logical reference; and performing handover signaling with theaccess network node including receiving an assigned target frequencywhich is a second logical reference for the physical frequency.
 10. Themethod of claim 9, further comprising the wireless terminal device:analyzing mapping of the first and second logical references to observethat they relate to the same physical frequency; and in response toobserving that they relate to the same physical frequency, recoveringmeasurement values made for the first logical reference and assigningthe measurement values for the second logical reference.
 11. The methodof claim 9, wherein the logical references are evolved UMTS (UniversalMobile Telecommunications System) Terrestrial Radio Access (EUTRA)Absolute Radio-Frequency Channel Number (EARFCN).
 12. The method ofclaim 9, wherein the performing handover signaling comprises receiving ameasurement configuration including the second logical reference. 13.The method of claim 9, further comprising the wireless terminal deviceperforming the handover such that the wireless terminal device operateson the physical frequency using the second logical reference after thehandover.
 14. A wireless terminal device of a carrier aggregationenabled cellular wireless communication system, where a same physicalfrequency on which the wireless terminal device interacts with an accessnetwork node of the cellular wireless communication system has more thanone logical reference, the wireless terminal device comprising:processing circuitry; memory containing instructions executable by theprocessing circuitry whereby the wireless terminal device is operativeto: perform an operation where a need for an inter-band handover occurs,wherein the wireless terminal device currently operates using a firstlogical reference; and perform handover signaling with the accessnetwork node including receiving an assigned target frequency which is asecond logical reference for the physical frequency.
 15. The wirelessterminal device of claim 14, wherein the instructions are such that thewireless terminal device is operative to: analyze mapping of the firstand second logical references to observe that they relate to the samephysical frequency; and in response to observing that they relate to thesame physical frequency, recover measurement values made for the firstlogical reference and assign the measurement values for the secondlogical reference.
 16. The wireless terminal device of claim 14, whereinthe logical references are evolved UMTS (Universal MobileTelecommunications System) Terrestrial Radio Access (EUTRA) AbsoluteRadio-Frequency Channel Number (EARFCN).
 17. The wireless terminaldevice of claim 14, wherein the performing the handover signalingincludes receiving a measurement configuration including the secondlogical reference.
 18. The wireless terminal device of claim 14, whereinthe instructions are such that the wireless terminal device is operativeperform the handover is such that the wireless terminal operates on thephysical frequency using the second logical reference after thehandover.